High Vacuum Furnace Research Articles

Brazing of Porous Nickel to Copper and Stainless Steel: Microstructure and Mechanical Properties

A porous nickel (Ni) was brazed to copper (Cu) and stainless steel 304 (SS304) using VZ2250 and MBF67 brazing filler metal with a composition of 77.4Cu-9.3Sn-7.0Ni-6.3P and 64.5Ni-25Cr-6P-1.5Si (Cu: Copper, Sn: Tin, Ni: Nickel, P: Phosphorus, Cr: Chromium, Si: Silicon), respectively for joint microstructure and mechanical properties analysis. Porous Ni with a pore density of 15 pores per inch (PPI) was sandwiched between Cu/VZ2250 and MBF67/SS304. A brazed joint of Cu/Porous Ni/SS304 with VZ2250 and MBF67 brazing filler metal was prepared in a high vacuum furnace at different brazing times of 5, 10, and 15 minutes for 1015 °C with a heating and cooling rate of 10 °C/min, respectively for comparison purpose. The microstructure and mechanical properties of the brazed joint were investigated to identify the joint ability after the brazing process. Scanning Electron Microscope (SEM) equipped with Energy Dispersive X-Ray Spectroscopy (EDS) confirmed the interfacial microstructure by the formation of the diffusion filler metal (dark grey colour) for the Cu/Porous Ni/SS304 with VZ2250 and MBF67 brazing filler metal. For shear strength tests, the value decreases with an increase in the brazing time. The shear strength tests for the brazed joint of Cu/Porous Ni/SS304 with VZ2250 and MBF67 brazing filler metal show the maximum shear strength test value can be achieved for the brazing time of 5 minutes. The decreasing shear strength value was observed with differences in structural data of porous Ni due to the softening after the brazing process. Keywords: Brazing, Microstructure, Porous Nickel, Shear Strength.

Modal analysis for the non-destructive testing of brazed components

Abstract In brazing processes, the formation of defects within the brazing joint due to deviations in brazing process and material is a recurring problem. These affect the component quality as well as the component properties. In this study, modal analysis is fundamentally investigated as a potential tool for non-destructive testing of brazing joints as well as for fast quantification of the precision of the brazing process. The aim of the investigation is to detect defects in brazed components. For this purpose, test specimens in defect-free and defect-containing form are brazed by means of a high-vacuum furnace. The subsequent recording and real-time analysis of the oscillation behavior of these test specimens is to be used to evaluate the quality of these brazed joints. A method, developed specifically for this purpose, automatically evaluates the recorded oscillation profile based on several defined frequency positions. For the first time, the results show that a reproducible classification of brazing seam quality into OK and not-OK can be made by comparing several frequency positions with already known oscillation profiles.

Optimization of brazing process and structure lightweight design for diamond microchannel

The application of diamond material significantly improves the heat dissipation capability of liquid cooling microchannels, solving the bottleneck problem of heat dissipation for highly integrated electronic components and thus promoting the development of a new generation of military electronic equipment. In this study, diamond microchannels with ultra-high heat flux density were reliably vacuum-brazed by using AgCuTi filler metal in a high vacuum furnace. Microstructure and properties of diamond brazing joints were studied and effect of brazing temperature and time was analyzed. The optimal brazing process parameters were obtained as follows: a vacuum level of <1×10−5 Pa, brazing temperature of 840°C, brazing pressure of 0.5–3 bars and holding time of 10 min. Following vacuum-brazing experiment, the brazing residual stress and working stress of the diamond microchannel were analyzed by finite element simulation. The wall thickness of the diamond microchannel was optimized. The minimum wall thickness, which was 0.4 mm, was obtained for the diamond microchannel with dimensions of 14 mm × 10 mm × 1.3 mm. On that basis, the influence of brazing pressure on the brazing filler overflow in the diamond microchannel brazing process was studied. It was showed that when the pressure was below 1 bar, the overflow of brazing filler from the brazing seam could be controlled to a minimum, especially suitable for brazing precision. The formation of residues in the diamond microchannel was thereby avoided basically, and a diamond microchannel heat sink with good performance was obtained.

Wear characteristics of brazing diamond abrasive wheel on high efficiency grinding ferrous metals

A kind of diamond abrasive grinding wheel was brazed in high vacuum furnace using Ni–Cr–P–Si active powder filler alloys. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Raman spectra and X-ray diffraction (XRD) technique analysis were applied to investigate the wear characteristics of brazing abrasive grinding wheel during the process of dry cutting ferrous metal and the interface characteristics of brazing diamond grains to steel substrate. The reaction products such as Cr7C3 and Cr3C2 carbides with columnar shape were formed toward around the diamond brazed interface. The results showed that diamond brazing abrasive wheel had an advantage in terms of more high efficiency and safety than resin grinding wheel during the process on cutting ferrous metals. The main tool wear model was abrasive grains broken, fracture and corrosion which were near the brazed interface. It revealed that the cutting chips were adhered to the surface of broken grains and covered the abrasive grits during the cutting process where arising high temperature on the grinding arc zone. Results proved that the graphitization phenomenon of diamond grits was slightly occurred and the diamond bonding strength was strong enough to meet the requirements of high efficiency and heavy load machining on dry cutting cast iron. The experiment also demonstrated that a kind of safety, high strength and super sharp diamond abrasive wheel could raise machining efficiency on cutting ferrous metal materials.

Cutting of Diamond Substrate Using Fixed Diamond Grain Saw Wire.

This study demonstrates that a single-crystal diamond substrate can be cut along designed lines using the diamond-saw-wire cutting method. We developed an original saw-wire fixed diamond-grain using a bronze solder with a high melting temperature. We created a unique product machine system with a high vacuum furnace and a bronze solder that contains a metallic compound. The diamond cutting mechanism employed in this study is based on the mild wear phenomenon, owing to the friction between the diamond surfaces. A linear relationship between the cutting length and wire feed distance was observed. The relationship can be approximated as y = 0.3622x, where y (μm) is the cutting depth and x (km) is the wire feed distance. The life of the saw-wire was longer than that of the 6000 km wire feed distance and was tested by reciprocating an 8-m short wire at a speed, tension, and cutting force of 150 m/min, 1 N, and 0.2 N, respectively. A single crystal diamond substrate could be cut along the designed line, which was more than 2 mm long. The cutting speed was maintained constant at 0.36 μm/km.

Influence of Gas Temperature and Heat Treatment on Microstructure and Properties of Cold Sprayed Commercially Pure Titanium

Diffusion of oxygen and nitrogen in the cold sprayed commercially pure Ti (CS CP Ti) deposits profoundly impacts their mechanical properties. One plausible approach to additively manufacture a malleable (wrought) and high-density Ti is optimizing CS deposition parameters considering a reduction in porosity for the following heat treatment. Herein, we examined porosity, bulk density, and hardness characteristics of CS CP Ti deposits produced at varying processing gas temperatures (700, 800, and 900°C), which significantly influences the interactions of CP Ti with oxygen and nitrogen. Post-processing heat treatments at 800, 900, and 1000°C were performed in a high vacuum furnace, respectively, which diminished splat boundaries and submicron pores with increasing grain size. SEM images revealed that CS CP Ti had a dense microstructure with low porosity. According to LECO research, low spraying temperatures (i.e. 700°C) maintained oxygen and nitrogen levels in the CS CP Ti deposits at the same level as the stock powders. The bulk density of CS CP Ti produced at 900 °C matched that of wrought CP Ti metal. In addition, to improve the mechanical properties of CS CP Ti deposits, we looked at the link between CS conditions and heat treatment.

Method for in situ texture investigation of recrystallization of Cu and Ti by high-energy synchrotron X-ray diffraction

Abstract High-energy synchrotron radiation has been used to study in situ annealing of cold-rolled Cu and Ti. The measurements were performed using a high-vacuum furnace in transmission geometry and an area detector. The diffraction images were subsequently processed to extract the orientation distribution. The recrystallization process could be followed with a time resolution of the order of 10 s, and good pole figures could be obtained from the very limited amount of data in single diffraction images. The pole figures compare favorably with pole figures of the same material measured ex situ with a conventional pole figure goniometer. For Cu, a rapid and complete change from a typical rolling texture to a cube texture was observed after annealing for 20 min at 650 °C. For Ti, changes were more subtle with a tendency for c-axes to diminish near the normal direction, as well as for a-axes to become aligned with the rolling direction. The method makes it feasible to study the kinetics of recrystallization with quantitative texture analysis.

Interface characteristics and mechanical properties of vacuum-brazed diamond with Ni–Cr+W composite filler alloy

In this study, the diamond was vacuum-brazed to AISI 1045 steel using Ni–Cr + W composite alloy in a high-vacuum furnace. Tungsten in alloy reduces the covering of diamond, leading to the increase in its exposed height. Mechanical performance tests confirmed that static pressure strength and impact toughness of diamond brazed using Ni–Cr + W composite alloy are 18% and 7% higher than those of diamond brazed using common Ni–Cr alloy, respectively. Moreover, the degree of graphitization of the diamond brazed with Ni–Cr + W composite alloy decreases, and its thermal residual stress gets reduced by 11%. Scanning electron microscopy system equipped with energy-dispersive spectrometer and X-ray diffraction were used to investigate interfacial microstructure of brazed diamond. Results indicate that metallurgical bonding is still formed between diamond and composite alloy, so that diamond grains exhibit a high holding force. Furthermore, tungsten can react with both the diamond and the alloy without causing any separation in brazed joint. At the same time, tungsten combines with a certain amount of nickel, which reduces graphitization degree of diamond and improves its integrity.

Формирование интерметаллидных покрытий при использовании плазмы олова и ниобия методом магнетронного напыления

Some regularities in the formation of niobium-tin coatings using magnetron sputtering have been studied. The coatings were obtained both by layer-by-layer and simultaneous deposition from two plasma sources. The optimal mode of operation of the magnetron source was determined to ensure the surface concentration of tin at the level of 19-26 at.%. The elemental composition and microstructure of the obtained films have been studied. A study was made of the structural-phase composition after annealing of the samples in a high-vacuum furnace at a temperature of 800°C. The research results indicate the formation of an intermetallic phase of triniobium stannide, while the best results in terms of the expected superconducting properties were obtained in the mode of simultaneous coating deposition.

Армированные одностенными углеродными нанотрубками композиты на основе ZrO2, полученные свободным вакуумным спеканием

The results of a study of sintered composites based on yttria-stabilized zirconia (ZrO2) reinforced with single-walled carbon nanotubes (SWCNTs) are presented in this paper. Mixing of ZrO2 nanopowder with SWCNTs was carried out in ethanol using an ultrasonic bath and a magnetic stirrer. Composite powders with 0.1, 0.5 and 1 wt.% SWCNTs and ZrO2 nanopowder were pressed into compacts at a pressure of 100 MPa, and then they were sintered in a high temperature vacuum furnace for 2 h at a temperature of 1500°C with a heating rate of 300°C / h. Changes in the microstructure, phase composition, and mechanical properties were investigated depending on the SWCNT content in the samples. It was found that in the selected sintering mode, high density samples (99.2 – 97.5 %) were obtained. It was found by scanning electron microscopy that undivided, entangled SWCNT bundles / aggregates and individual nanotubes, which together formed a continuous reinforcing structure, were observed in the microstructure of the composites. Moreover, SWCNTs led to the refinement of the microstructure of composites; the average grain size of composites was 16 % lower than that of ZrO2 ceramics. It was found by X-Ray diffraction that only high temperature modifications of zirconia (cubic and tetragonal) were present in ZrO2 ceramics and composites, and SWCNTs led to a slight decrease in the size of coherent scattering domain. It was found by the Vickers indentation method that the composite based on ZrO2 with 0.5 wt.% SWCNT was optimal in terms of mechanical properties, since it had the highest microhardness (13.6 GPa, which was 6 % higher than that of ZrO2 ceramics) and had a 12 % higher fracture toughness.

High-Temperature Nanoindentation of an Advanced Nano-Crystalline W/Cu Composite.

The applicability of nano-crystalline W/Cu composites is governed by their mechanical properties and microstructural stability at high temperatures. Therefore, mechanical and structural investigations of a high-pressure torsion deformed W/Cu nanocomposite were performed up to a temperature of 600 °C. Furthermore, the material was annealed at several temperatures for 1 h within a high-vacuum furnace to determine microstructural changes and surface effects. No significant increase of grain size, but distinct evaporation of the Cu phase accompanied by Cu pool and faceted Cu particle formation could be identified on the specimen′s surface. Additionally, high-temperature nanoindentation and strain rate jump tests were performed to investigate the materials mechanical response at elevated temperatures. Hardness and Young′s modulus decrease were noteworthy due to temperature-induced effects and slight grain growth. The strain rate sensitivity in dependent of the temperature remained constant for the investigated W/Cu composite material. Also, the activation volume of the nano-crystalline composite increased with temperature and behaved similar to coarse-grained W. The current study extends the understanding of the high-temperature behavior of nano-crystalline W/Cu composites within vacuum environments such as future fusion reactors.

Oxidation and phase transformation behaviors of Si3N4-xMgAl2O4 (0

This research investigates the oxidation behavior of nanocrystalline/amorphous Si3N4 compounds in atmospheres with different oxygen pressures. High purity nanocrystalline/amorphous Si3N4 and MgAl2O4 mixtures were used to investigate oxidation behavior of Si3N4. Si3N4-xMgAl2O4 (0 < x < 90 wt.%) samples were prepared with mixing in a jar mill, followed by pressing and heating in a high vacuum furnace. Specimens were characterized using FE-SEM, EDS, XRD, FT-IR, and ICP. Thermal analysis (TG/DSC) was also employed to investigate the thermal behavior of samples in different atmospheres. Results showed that phase transformation in pure Si3N4 is controlled by holding time and oxygen pressure in the atmosphere. Results also showed an increase in the weight of pure Si3N4 by 5.3 and 15.2 % for 0.5 and 2 h in a vacuum atmosphere, respectively, inferring that crystallization reaction proceeds with holding time. In the temperature range 1000–1400 °C, a noticeable exothermic peak has appeared for pure Si3N4 in the air atmosphere which was attributed to the formation of cristobalite (SiO2) phase. Besides, thermal analyses of Si3N4-xMgAl2O4 (0 < x < 90 wt.%) samples in the nitrogen atmosphere showed that the maximum weight change was attained in the Si3N4-50% MgAl2O4 sample. Mechanisms and implications of oxidation in all cases are thoroughly discussed.

Microstructural and Mechanical Characterization of W-CuCrZr Joints Brazed with Cu-Ti Filler Alloy

The determination of the mechanical properties of a brazed joint is an important factor to reach the metallurgical level of a joint development. This paper evaluates the mechanical properties, and its correlation with the joint microstructure, of a W-CuCrZr joint brazed in a high vacuum furnace using 80Cu-20Ti flexible filler material in tape form. This joint is meant to be implemented in the divertor application in future fusion power plants. Main experimental parameters were a brazing temperature of 960 °C and a dwell time of 10 min. The microstructure of the joint was constituted by Cu solid solution and Cu4Ti phases. This last phase was distributed in the W-braze interface. Mechanical properties were evaluated by means of Vickers microhardness and mechanical tests by applying pure shear loads. The microhardness profile of the brazed joint indicated that W remained with the as-received hardness but CuCrZr base material was softened after the brazing procedure. Shear strength of 96 ± 15 MPa was obtained for the brazed joint and fracture propagated at the W-braze interface.

Development, optimization, and characterization of NiCrBSi-TiB2 flame-sprayed vacuum fused coatings

The post-treatment of thermally sprayed Ni-based coatings is extremely important to deliver highly qualitative components. NiCrBSi-TiB2 mechanically mixed powder in four different volumetric concentrations was flame-sprayed onto S355JR steel and post-processed in a high temperature vacuum furnace. The holding time and temperature of the heat treatment was optimized through a central composite design and the concentration delivering the best results was selected for further examination. The microstructural complex and dense obtained coating presented a strong metallurgical bonding at the interface region with a high interface fracture toughness. Tribological and corrosion tests were additionally performed in comparison with a NiCrBSi flame-sprayed coating as reference sample. Non conformal pin-on-disc tests showed that although the coefficient of friction of the two tested samples was similar, the wear rate of both sample and counterpart of the TiB2 containing coating was significantly lower. Electrochemical tests in 3.5% NaCl solution showed that the alloyed coating exhibits lower corrosion current densities and a more positive breakdown potential than the reference sample. A negative effect of addition of TiB2 ceramic particles to the Ni-based coating regarding its corrosion behaviour in a chlorine containing environment could not be established.

Effect of B on improving wetting and imbibition of sintered porous Ta by Cu melt

The present study focuses on the interaction between copper melts and porous tantalum plates (purity, 99.99 wt% Ta). The samples were prepared by sintering tantalum powder with different grain size and were characterized by 65% porosity. A procedure to perform direct observations of the interaction between the melt and plates was developed. Equipment for high-speed recording of dipping of the samples into the melt was designed. The frame rate was up to 5000 fps. A high-vacuum furnace with a graphite heater was used. Wetting experiments were performed in the temperature range of 1100–1400 °C.As expected, at temperatures near 1150 °C the tantalum cake coated with an oxide layer is not wetted by pure copper and does not imbibe it. Rising temperature slightly improves wetting. Doping the copper melt with 2 at.% B at 1150 and 1275 °C reduced the contact angle to 60° it dropped below 25° at 1400 °C. The reason for the observed phenomenon was that doping with boron results in reactive wetting and formation of tantalum boride. Wetting of the porous samples was compared to wetting of cast tantalum plates.The kinetics of imbibition with Cu(B) melt were recorded. The imbibition dependence changed from power-law to linear one as temperature increased from 1275 to 1400 °C. This behavior is associated with degradation of the tantalum boride layer.

Diffusion-bonded pulsating heat pipes: fabrication study and new channel proposal

In the present work, diffusion bonding technology used for fabrication of pulsating heat pipes (PHP) in a high-vacuum, high-pressure and high-temperature furnace is discussed. Seven different configurations of PHPs were manufactured, subjected to different fabrication parameters. PHPs with 10 and 26 parallel channels of circular and square cross-sectional areas were constructed. In addition, a PHP with a novel cross-sectional channel geometry, composed by a circular area with lateral grooves, which is easily fabricated by the present technology, is proposed. The deformation of the geometries of the channel cross sections was observed. The square channel PHP showed large deformation, while the deformations of the circular ones, including the new proposed geometry, were small. The distribution of the PHPs along the matrix in a single bonding cycle showed to be a very important parameter: Those PHPs produced in parallel presented some deformation and leakage problems, while those made by stacking mode did not presented any leakage. Scanning electron microscopy and optical microscopy were used to assess that diffusion bonding is a very suitable and promising technology for the fabrication of PHPs. The thermal tests showed that the grooved circular channel PHP presents higher thermal performance.

Effects of multiwall carbon nanotubes on dielectric and mechanical properties of CaCu3Ti4O12 composite

This work reports the synthesis of calcium copper titanate (CaCu3Ti4O12)/multiwall carbon nanotubes (MWCNT) composites using ultrasonic technique followed by sintering in a high vacuum furnace. The effect of MWCNT content (0.05, 0.1, 0.15, and 0.2 wt%) on the structural, dielectric, and mechanical properties of CaCu3Ti4O12 (abbreviated as CCTO) were investigated by TEM, XRD, FTIR, FESEM-EDAX, dielectric measurement, as well as tensile strength and flexural strength tests. XRD patterns revealed that the MWCNT loading did not affect the phase structure; however, the average crystallite size (D) was reduced from 60.88 nm to 40.79 nm. The samples had porous structures and the porosity reduced from 45.57% to 40.73% with MWCNT loading. The dielectric and mechanical properties of CCTO were enhanced with an increase in MWCNT loading. An important observation was that the CCTO mixed with 0.2 wt% MWCNT exhibited the highest dielectric permittivity (εr = 27,768) and the lowest dielectric loss (tan δ = 0.52) at 1 kHz. With the addition of 0.2 wt% MWCNT, the values of load, tensile, and flexural strength increased to 10.38 kN, 101.88 MPa, and 275.07 MPa, respectively, due to improvement in densification. These outcomes have values for the fabrication of CCTO and the optimization of its performance for electronic devices such as capacitors and antennas.

Development of a brazing procedure to join W-2Y2O3 and W-1TiC PIM materials to Eurofer

The present work proposes a brazing technique to address both the mechanical and metallurgical requirements of joining two different tungsten powder injection moulding materials (W-2Y2O3 and W-1TiC) with Eurofer steel. The joining procedure uses pure copper as a filler material and the brazing parameters are 1135 °C for 10 min in a high vacuum furnace. Metallurgical evaluation indicates the achievement, in both cases, of 100% metallic continuity at the interface. The brazing temperature is high enough to activate diffusion phenomena at the interface, giving rise to strong adhesion properties. The mechanical properties are evaluated by shear strength tests with values of 163 ± 55 and 162 ± 6 MPa for W-2Y2O3/Eurofer and W-1TiC/Eurofer, respectively. These values are considerably higher than those obtained in previous works using other interlayer materials. The microhardness of these W-base materials is similar to that in the as-received condition, indicating that it was not affected by the brazing process.

Synthesis of powder metallurgy Ti-3Fe-2Al alloy using high-frequency induction heating

A powder metallurgy approach was applied for the synthesis of an [Formula: see text] Ti-2Al-3Fe alloy. Blends of the elemental Ti, Al and Fe powders were compacted and subsequently sintered. High-frequency induction heating (HFIH) instead of conventional high-vacuum furnace heating was used for the sintering, due to its high efficiency. The effect of temperature on the level of densification, residual porosity and mechanical properties was studied. Electron dispersive spectrum analysis was used to study the dissolution and homogenization of the alloying elements. The results showed that a short induction sintering (IS) cycle in the range of 10–15 min is sufficient to achieve significant powder consolidation, evident by the increase of the density and mechanical properties. The residual porosity diminishes with the increase of the sintering temperature. Full dissolution of the alloying powders is completed after sintering at temperatures above those of [Formula: see text]- to [Formula: see text]-phase transformation.

Interfacial analysis of vacuum brazing diamond/WC mixed abrasives with Ni[sbnd]Cr[sbnd]B[sbnd]Si active filler

To develop a new generation of super–hard abrasive tools, diamond/tungsten carbide (WC) mixed abrasives were brazed onto AISI 1045 (0.45% C) steel substrate by using NiCrBSi active filler alloy in a high vacuum furnace. The brazing operation was executed at three different temperatures (1010 °C, 1030 °C, and 1050 °C), with different dwelling times (10 min, 15 min, 20 min, 25 min and 30 min). Scanning electron microscopy, energy dispersive spectroscopy and X–ray diffraction analysis were used to investigate the interfacial characteristics of the brazed diamond/WC mixed abrasives. The results of microstructural analysis showed that several chemical and metallurgical reactions occurred between NiCrBSi active alloy and diamond/WC mixed abrasives have occurred during the brazing process. Cr3C2 and Cr7C3 compounds were generated at the brazing interface of diamond and the active alloy. At the same time, the Ni2W4C and NiW and Cr7C3 phases were formed between WC and the active alloy. The bonding force test of the brazed joints was carried out and the results demonstrated that the newly developed brazing tools can be applied in the field of iron material processing with high efficiency and longer working life.